Preheat your oven to 425°F (220°C). Lightly butter a 12-cup muffin tin or line it with paper liners.

To make the streusel: Combine the shredded coconut, brown sugar, flour, and cold butter in a food processor. Pulse until the mixture forms a crumbly texture with unevenly shaped pieces. Alternatively, use your fingertips, a fork, or a pastry cutter in a mixing bowl to achieve the same result. Cover and refrigerate until ready to use.

To make the muffins: In a large bowl, sift together the flour, baking powder, baking soda, salt, and cinnamon. Stir in the sugar until evenly combined.

In a separate medium bowl, whisk the eggs, yogurt, oil, and vanilla extract until smooth. Pour the wet mixture into the dry ingredients and gently stir with a wooden spoon or rubber spatula until just combined. The batter will be thick and slightly lumpy—do not overmix. Carefully fold in the mango cubes and pecans, if using.

Divide the batter evenly among the muffin cups, filling them nearly to the top. Sprinkle each muffin generously with the chilled streusel mixture. Place the muffins in the oven and bake at 425°F (220°C) for 3 minutes. Then, reduce the oven temperature to 350°F (180°C) and continue baking for an additional 12–17 minutes. The muffins are done when a toothpick inserted into the center comes out clean. If the streusel begins to brown too quickly, loosely cover the muffin tin with aluminum foil.

Allow the muffins to cool in the pan on a wire rack for about 10 minutes. Then, remove them from the tin and let them cool completely on the rack.

Mango muffins are at their best when enjoyed on the day they are baked. However, they can be stored in an airtight container at room temperature for 2–3 days or frozen for up to 2 months.